1. Field of the Invention
The present invention pertains to methods and apparatus for recovery, purification and reinfusion of blood lost at a wound site, either during a surgical or postsurgical management period. More specifically, the present invention applies to aspiration of shed blood from a wound site during intraoperative or postsurgical recovery periods, on-line purification of aspirated blood by filtration and cell-washing using membranes, and reinfusion of purified autologous blood to the patient on a real time basis. With some modifications, the present invention may be used as a hemofiltration or ultrafiltration system for the treatment of acute and end-stage renal diseases.
2. Statement of the Art
Significant blood loss to a person may occur during a traumatic injury, such as an auto accident, or during a serious and traumatic surgery, such as open heart surgery, or during a postsurgical recovery period due to hemorrhagic conditions. Significant loss in blood results in decreased blood pressure, decreased cardiac output, and decreased oxygen delivery to tissues, particularly brain cells. For these reasons, it is necessary to compensate the loss in blood by transfusing the patient with blood as soon as possible.
During an intraoperative period, a pool of shed blood accumulates in the wound site which obstructs the surgery site unless it is aspirated out therefrom. Usually, suction is provided to remove the shed blood, other accumulated fluids, blood clots and other tissue debris. The total loss of blood may vary from 1,000 ml to 15,000 ml depending on the extent of the surgery and the attendant traumatic conditions.
During a postsurgical recovery period due to hemorrhagic conditions, the closed wound may continue to bleed into the chest, pleural cavity, or abdominal cavity. On an average, 1,000 ml of blood is usually lost over a five hour period. However, blood loss could conceivably be as high as 21,350 ml. In such instances, the patient may have to be rushed back to surgery to correct the underlying problem. It is obvious that blood transfusion is imperative under such conditions. Usually, the shed blood is drained from the body cavity using drainage tubing under a controlled suction. The drained blood is generally collected in a container.
Blood shed during intraoperative or postsurgical recovery periods can be collected in a container and reinfused to the patient provided the salvaged blood is free of impurities. Typical impurities are blood clots, tissue debris, hair, foreign particles, activated coagulation factors, denatured proteins, plasma free hemoglobin, and any other fluids (e.g. irrigation fluid) that are being introduced into the wound site by medical personnel.
Impurities in salvaged blood are conventionally filtered out using a 40 micron filter to remove particles greater than 40 microns in size, and the blood is then subjected to "cell washing." The cell washing technique may involve mixing blood with a physiological solution (e.g., saline or Ringer's) in equal proportion to the blood. The blood is then centrifuged to recover the heavier blood cells which are suitable for reinfusion to the patient. The lighter portion of the centrifuged fluid (i.e., the top portion of the centrifuge tube content) containing platelets, white cells, plasma proteins and antibodies is usually discarded as waste. This is a significant loss to the patient, particularly the loss of coagulation factors, platelets, white cells and antibodies. Therefore, the efficiency of recovery of blood products by conventional cell washing techniques is low. Additionally, conventional blood recovery methods are not accomplished on-line, and in real time. Rather, they are batch processes involving operator intervention, and are subject to human errors and time delay.
Thus it will be appreciated that purification of salvaged blood based on cell-centrifuge machines are not designed to work on a real time basis. That is, there is considerable lag time (more than 15 minutes) between the moment of aspiration of blood and reinfusion of processed autologous blood. This is a significant problem, especially when the patient bleeds rapidly, and his/her lost blood volume needs to be compensated immediately. Furthermore, during cell washing by the centrifuge technique, a significant amount of red blood cells are lost, and almost all white blood cells, platelets and plasma proteins including antibodies.
Due to the aforementioned problems in the conventional cell washing technique, a patient is usually given homologous (donor) blood transfusions rather than his/her own blood, which is still being processed.
Problems with homologous blood transfusion are many. The major problem is providing suitable donor blood which will not cause side effects, such as anaphylactic reactions, and which does not contain donor-associated infections, such as hepatitis, malaria, or acquired immune deficiency syndrome (AIDS). At times, it is difficult to find appropriate types and amounts of blood necessary for transfusions, and it can become very expensive.
Due to the aforementioned problems, "autotransfusion" (reuse of a patient's own blood) has received significant attention. A number of autotransfusion systems have been developed in recent years with varying system configurations. They are composed of three basic units; an aspirator unit, a cell washing unit, and a reinfusion unit.
The typical aspirator unit consists of a suction handle attached to suction tubing which is connected to an emboli filter reservoir. The emboli filter is generally provided with an air vent line, a degassifier, a filter, and a blood reservoir. Controlled suction is usually applied with a vacuum source via a vent line. The vacuum aspirates shed blood, along with other impurities, from the wound site. Larger impurities are trapped in the emboli filter.
Filtered blood is usually pumped to a cell centrifuge machine where it is mixed with an appropriate "washing fluid" and centrifuged for a specified time period until the heavier blood cells are separated from the plasma. This method is typically cumbersome, time consuming, and requires an operator to attend to the system continuously. Furthermore, there is a loss of precious plasma proteins, antibodies, and white blood cells which are important for the body's ability to fight infection. Thus, it would be an advancement in the art to provide on-line, continuous methods and apparatus for blood purification which would minimize loss of precious blood elements, and would reinfuse to the patient his/her own blood on a real time basis. It would be a further advancement to provide an automatic system which would reinfuse whole blood at a specified hematocrit level free of air emboli.
The aforementioned prior art systems are designed to be used during surgery (i.e., intraoperative period). During the post-surgical recovery period, bleeding may still continue from the closed wound, but at a significantly reduced flow rate. Bleeding usually progresses at about 1,000 ml over a five hour period. Post-surgical autotransfusion of shed blood is particularly useful in postoperative management of patients with serious hemorrhage. Post-surgical blood losses may range from 2,050 ml to 21,350 ml. The shed blood is usually drained using a drainage unit by a controlled suction.
There are many chest drainage units on the market. Examples are the "Pleur-evac" chest drainage unit by Deknatel, Howmedica, Inc., New York; "Sentinel Seal Compact" "chest drainage unit" by Argyle; "Snyder Hemovac Compact Evacuator", Zimmer Corp., Dover, Ohio; and "Sorenson Autotransfusion System", Salt Lake City, Utah. In all these drainage units, a controlled suction (i.e., where negative pressure does not exceed -25 Cm of water) is applied to drain the shed blood from the closed wound site via one or two drainage tube. The drained blood is filtered to remove solid particulates and is collected in a bag. When a suitable volume of blood is collected, it can be reinfused to the patient directly without washing the blood cells, or it can be reinfused to the patient after it is washed with saline solution using a cell centrifuge machine. A 40 micron filter (e,g., a "Pall filter") is typically used during reinfusion of the blood. Care is taken to protect the closed wound from excessive negative pressure (e.g., greater than -20 Cm water), and to minimize the blood-air interface.
None of the aforementioned systems wash the blood on-line; rather, the washing needs to be done in a batch operation using a cell centrifuge. Since a controlled suction is applied to the drainage tubing using a vacuum pump, the blood-air interface is not completely eliminated in those systems. Thus, it would be an advancement in the art to provide an automatic post-surgical autotransfusion system which eliminates the problems described above.